A diaphragm seal system in vacuum pressure process must master a significant challenge ? it must deliver a reliable measuring result, even though the pressure drops and the temperature rises as well. The exemplory case of a chemical company producing phthalic anhydride (PA) shows that it is in no way self-evident that requirement could be met on a frequent basis.
PA is primarily used as a plasticiser for plastics. However, it is also found in the production of synthetic resins and dyes. The plant operator obtains this compound via the catalytic oxidation of o-xylene in the gas phase, followed by vacuum pressure distillation process.
Critical phase for pressure measurement
In this process, the critical phase for pressure measurement occurs in the distillation column. There, the procedure temperature can rise to more than 230 �C while the pressure drops to 100 mbar abs. With this type of contrary action, the traditional installed measurement technology reaches its performance limit relatively quickly, that your aforementioned manufacturer was forced to learn ? all instrumentation showed a measurement deviation outside the defined tolerance after only fourteen days.
Diaphragm seal system adapted in all elements to the vacuum process
The diaphragm seal system is tailored exactly to the conditions of the vacuum process and tested under application conditions.
Consequently, the company approached WIKA with the obtain a measuring solution that would also fulfil its task with the required accuracy in the long term beneath the conditions described. WIKA then drew on its in-depth expertise to create a diaphragm seal system for the vacuum process, comprising an activity transmitter (model IPT-20), a flange-type diaphragm seal with flush diaphragm (model 990.27) and a capillary.
All elements of this measuring system were selected designed for the application form. Silicone oil KN32 was therefore selected as the fill fluid for pressure transmission. The cleaning and conditioning of the diaphragm seal, the capillary, the connection pieces plus the automated filling process were also matched to each other exactly. With sensitive limit ranges, even one drop of liquid an excessive amount of or too little can destabilise the quantity balance of the diaphragm seal system and thus impair its function. Due to this fact, correct measurement would no more be guaranteed.
Faux Pas under application conditions
After cleaning, all elements of the diaphragm seal system were first fully welded into a single unit as usual, accompanied by the filling and adjustment of the machine. Before delivery, however, there is another crucial step ? in its laboratory, WIKA simulated vacuum pressure process for the diaphragm seal system in accordance with the customer?s conditions and subjected it to a thermal ageing process. This test confirmed the procedure suitability of the measuring system.
Note
Unpopular on the WIKA diaphragm seal systems are available on the WIKA website. When you have any questions, your contact will gladly assist you to.
Also read our posts
Diaphragm seals for stable flow measurement in deep seas
Just how do diaphragm seals work?
Watch the following video to learn more concerning the functionality, application areas and advantages of diaphragm seals: